Weight and balance training model



Jan. 31, 1950 c. F. DRowN ETAL 2,495,709

f WEIGHT AND BALANCE TRAINING MODEL Filed Aug. 20, 1946 2 Sheets-Sheet 1 MWA Jan. 31, 1950 c. F'. DRowN ETAL WEIGHT AND BALANCE TRAINING MODEL 2 Sheets-Sheet 2 `Filed Aug. 2o, 194e Igatentecl Jan.

WEIGHT ANI) BALANCE TRAINING MODEL Clifford F. Drown, Oklahoma City, Okla., Norman Zimmerman, Univer liam C. Ross, Dayton,

l6 Claims.

sity City, liao., and Wil-- Ohio Application August v20, 1946, Serial No. 691,674

l(Granted under the act of March '53, '11883, "as amended April :39, 1928; 370 '0. G. 757) The vinvention vdescribed herein may lbe manufactured and Vused by or for the Government for governmental purposes without payment tousol any royalty thereon.

This invention relates to small scale weight and balance airplane training models to aidin demonstrating visually to aircraft personnel' the effects of various load conditions.

It is an important factor in the operation 'and maintenance of aircraft that `the Vcenter of gravity (C. "G.) is kept within certain limits along the mean aerodynamic rchord "(M. A. C.) to obtain goodstability 'and controllability, and to avoid exceeding structural limits. Stability and contro-liability do not necessarily vary inthe same fashion. The movement ofthe C. G. to the vfront of the aircraft, as by load conditions, or to reduce tn'e C. G. in per cent M. A. C., will increase the stability butthis condition 4caribe exaggerated to the extent that 'less response will be obtained for the same amount of 'control force. /On [the other hand, increasing the C. "G. inper cent M. A. C. by movement of 'the C. G. toward 'the tail of the aircraft, as by load conditions, increases the response to 'control movement. Under either of these vconditions the C. G. can be moved to critical positions Valong the M. A. C. in which it is 'undesirable or dangerous for flying operation. The condition of good flight operation of la typical airplane appears to 'be with the C. within the approximate limits of '18% t0 34% M. A. C. order to get proper balance in flight. .A C. location within the above `vlimits `caribe obtained by proper location of the movable load.

In order that the C. G. in loading an Aairplane is maintained within the proper limits fto obtain good stability, controllability and Abalance the aircrew personnel should have some knowledge ofthe effects vof proper and improper loading.

The present invention makes it possible to .give

aircrew personnel a visual practical demonstration .of the eiects of various 'loading conditions and provides the instructor with vequipment yto establish various weight and balance problems, theory and engineering principles. The model demonstrates simulated typical aerodynamic Areactions using the relationships between static reactions. It has been found that the actual .demonstration with a small 4scale rmodel airplane supplemented by explanation give y.the trainees a fuller and better understanding of weight sand balance Yprinciples in aircraft ythan lectures, .-lms, posters, etc. It is `to be understood, however., that a vvcomplete and thorough scientic picture of weight and balance for night conditions cannot 2 be attained by such a Vmodel training aid since the aerodynamic moments of lforce and their eiiects on the airplane in night cannot be vtaken fully into account, Ibut for all practical purposes the weight and balance trainingfmo'del is valuable for demonstration.

"It 'is a principal object of vthis invention to provideza weiglitand'balance training airplane model foruse' in the demonstration of the effects of various loading conditions.

lt is another object of .this invention to provide a small rscale airplane model suspended from indicating .means in Aa v'iranien/ori: rto register the gross weight, Wing load, tail 'load and C. G. in per Scent M. A. C. `upon various loading .conditions oi the model.

- Itis a further object of this invention to provide a small scale model airplane, divided into station compartments, having kan adjustable hangar bracket meansattached in the a'irfoil adjacent .the fuselage .along the M. A. C. that is .connected to a'wng load indicator and arotatable sector `card bea-ringggross Weight and per-centM. A. C. scales in a framework, `and the elevator of the ymodel connected to a tail load .indicator and a pointer movable over `the gross `Weight and .per lcent M A. C. scale in the framework .for .suspending the model to demonstrate the gross weight, Wing load, tail load, C. G. vin :per cent M. A. Ci. .and elevator trim vposition asa result of various compartment loading conditions.

A still .furtherobject .of .ourinvention is to provide 4a framework housingwing load andr tail load indicators, the wing load indicator being operatively connected to a rotatable sector card in .the framework having gross Weight and per cent M. ..A. C. scales .thereon and the tail load indicator `operatively -connected to .a pointer movable .over the `faeeof .the sector card, afsmallscale air-plane model .having station compartments open to the exterior connected at its Wing portion 'to the wing load-indicator and its elevator connected to the tail vload indicator suspending it in Vthe f. framework to demonstrate the static veiects of weight distributed yin the kstation compartments by registering Ythe wing load and tail load `on the respective indicators, the gross Weight yand the CG. in per pent M. .AfCfby the position ofthe pointerover the gross fweight and per cent M..A.C.

scales `and 4the relative change in zelevatordelectionnecessary to trim the airplane 'for level-flight.

KOther objects .and a ffuller understanding fof the invention may behad by referring to the following :description andfclagims, taken =in conjunction With the accompanying drawings which shall partially broken away to reveal the construction p and arrangement of the indicators in the framework;

Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2; and

Fig. 4 is an enlarged partial view of the wing loa-d suspension bracket adjusting means with a part cut away to show the arrangements of parts.

Describing the invention more in detail and referring more particularly to Figs. 1, 2 and 3 in which there is shown a rectangular framework, of any preferred construction and generally referred to by the reference character I0, consisting of two upright members and I2, an upper cross member I3, and a lower cross member I4 substantially intermediate the ends of the upright members Il and I2. An indicator panel facepiece member l5 is secured on the frame members II, I2, I3 and I4 to form' an indicator enclosure I5 in the framework IU. The facepiece I5 has a central opening I1 closely resembling an isosceles trapezoid and two similar rectangular openings I8 and i9 on opposite sides of the central opening l1.

On the underside of the upper cross member I3, and within the indicator enclosure I6, are fastened three trunnion members 2|, 22 and 23 each being centrally located above the openings I1, I8 and i9, respectively. An isosceles triangular frarne 24 is pivotally mounted t0 the trunnion member 2| at the juncture of the equal sides and supports a sector card 25 having a gross weight scale 26 and percentage mean aerodynamic chord (per cent M. A. C.) scale 21 thereon visible through the central opening I1. Pivotally mounted in the trunnions 22 and 23 at the juncture of their equal sides are similar isosceles triangular frames 38 and 3|, respectively, supporting sector cards 32 and 33, respectively. The card 32 has a wing load scale 34 thereon, preferably graduated intc pounds, adapted to be visible through the opening I8 and generally referred to as the wing load indicator; and the card 33 has positive and negative tail load scales 35, 36 thereon, preferably graduated into pounds, adapted to be visible through the opening I9 and generally referred to as the tail load indicator. The openings |8 and I9 have arrowhead pointers 31 on their lower wall by which the respective indicator may be accurately read. The pivotal portions of the triangular frames 30 and 3| comprise of disc-like portions 38 and 39 with drilled holes 40 and 4I, respectively, therein spaced radially about the pivotal axis for the purposes that will later appear apparent. A substantially rigid rod 45 is pivotally connected at its opposite ends to the triangular frames 24 and 30 such that the sector cards bearing the Wing load and the gross weightper cent M. A. C. scales on these two triangular frames will turn simultaneously in the same rotative direction. A weight 45 is connected by a cord 41 operable over a pulley 48 that is rotatably supported on the framework member |2 by the trunnion member 49 to the triangular frame 30 to bias the triangular frames 24 and 30 in a clockwise direction. An indicator pointer 5| is mounted on a pivot 52 of a trunnion member 53 which is supported by the panel facepiece member I5. The indicator pointer 5| is adapted to sweep over the gross weight-per cent M. A. C. scaled sector card and includes cross needle pointers at the indicator end to form a gross weight needle pointer 55 and a per cent M. A. C. needle pointer 56 such that in any position of the indicato-r pointer 5I over the gross weight-per cent M. A. C. sector card the gross weight indication may be derived by comparing the needle pointer 55 with the gross weight scale 26, and the C. G. in per cent M. A. C. may be determined by the reference of the needle pointer 55 on the per cent M. A. C. scale 21. A disc-like portion 51 at the pivotal portion of the indicator pointer 5I is provided with holes 58 therein. A rod 59 has its opposite ends bent to pass through one of the holes 58 in the disc-like portion of the indicator pointer 5| and one of the holes 4| in the disc-like portion of the tail load triangular frame 3| on opposite sides of the pivotal axes such that a rotation of the triangular frame 3I in a clockwise direction will operate to rotate the indicator pointer 5I in a counterclockwise direction, and vice versa. The indicator pointer 5I has a horizontal extension 60 and a vertical extension 6| arranged about its pivotal axis for receiving weights to balance and dampen the tail load sector card and indicator pointer movement.

Suspended in the framework II'I below the indicator enclosure I6 is a small scale model airplane generally referred to by the character 1| (Fig. 1). The illustrated model is of the well known large four motor type but a model of any other type airplane may be used where desirable by using proper indicators for the particular model. The airplane model 1| shows just the essential elements to properly demonstrate the device and consists of the fuselage 12, airfoils 13, motor nacelles 14, flaps 15, rudder fin 16, stabilizer 11, elevators 18 and landing gear 19 and 89 whose purposes and functions are well known in the aircraft art. A quarter section of the fuselage 12 is cut away longitudinally to expose station compartments 8| for receiving weights representative of the load to be carried in the demonstration exercise. The airfoil 13 has an adjustable hanger bracket 82 in each of its sections adjacent the fuselage within the limits of the M.

A. C. that pivotally receives a rigid rod or strap.

at an opening 86 in the hanger bracket 82. The lower end of the rod or strap 85 is bifurcated at 81 to pass over the fuselage 12 to connect the hanger bracket 82 in each airfoil section. The upper end of the rod or strap 85 is lpivotally connected to the wing load indicator by having a portion bent to pass through one of the holes 40 in the disclike portion of the wing indicator triangular frame 33. Any downward load on the rod or strap 85 will actuate the wing load indicator and will rotate the gross weight--per cent M. A. C. sector card 25.

Referring to Fig. 4, each hanger bracket 82 is adjustably mounted (although those brackets may be mechanically connected to be actuated together) in each airfoil section in a direction parallel to the fuselage 12 within the limits of the M. A. C. for positioning the rod or strip 85 at the C. G. of the model along the M. A. C. Each hanger bracket 82 is integral with an internally threaded nut 9| within the airfoil 13 and slidable along a slot 92 in the upper surface of the airfoil. The nut 9| has a screw threaded connection with a screw threaded rod 93 that is held against endwise movement and adapted to be rotatedby usine a tool-as a ser@wdriver.inV the 1.ot94. or the .rod 93mm/ be knurled on the.

fluter.. end forturnins byhand. Integral` with the lhanger bracket 82 is a pointerv 95 that cooperais with, a per cent M. A. C. scale 96 on the, top surface of the airfoil 13, In` this particular illus tration the C. G. is arbitrarily chosen for this model to be 24% M, A. C. in which case the.

model 1| balances on the rod or ,Strap 85' by hangingv horizontally with the air .foils at the.

proper angle of attack. I

The elevator 18 is spring biased toa neutral position in which it will be in alignment with the stabilizer 11. On the elevator 18' at opposite sides of' the rudder iin 10 there is attached a Ieverarm, having its free end extending upward and' forward of the pivotal axis of the elevator'l. A substantially rigid rod or strap. I 01 ,hasA a bifurcation |02 at its lower endfto extend over the rud.. der iin 1B and pivotally connect eachclevator lever arm |00 at |03.. The upper end of the or strap |0| is bent to pass through one, of ythe holes 4| -in the disc-like portion 39 ofthe tailv load triangular frame 3| forward of its pivot such that a, downward pull on the element |0| causes the frame 3| to rotate counterclockwse, and an upward push on the element |`0| causesthe framev 3| to rotate, clockwise. The rods or straps' I 0| and 85 pass through openings prepared for them,V

inthe framework member I4. Any positive or negative tail, load of the model 1| willl produce a downward .or kupward force.. respectively., on, the. rod orstrap |0| and swing the tail load sector card 33-counterclockwise or clockwise, respective- 1y; to indicate thepositive, or negative load in pounds or the tail load indicator. @At the same time, theindicator pointer 5|l will be rotatedl across thegross weight-percent AC. scales 0fv the Sector Card. 25 in a clockwise or counterclockwise direction, respectively,` from which the percentage of C. G. along the A.. C. can be. determined by theneedle pointer 56. On the perf. cent A. C. scale 21, andthe gross vei'ght canbedtermined by the position of. the. cross needle. pointer 55 4on the Ygross weightA scale 2.5. Certain.

areas of the sector card scales 26 andgZ'l' may be colored) to indicate critical oonditions, ifdesir o able- (The landing wheels 19 and 80 areedapted to beA retractedk for dying conditions, or extended vtor' landing. as shown in dotted lines' Fie. l. to. demonstrate their reactiony on the'C;l G., wing load and tail load of the model.

y'Ille flaps 15 are also adapted. to be raised and loweredbut a true demonstration0i.` their influence on the C. G. cannot be .Shown by their moyement since the aerodynamic reaction is not considered,L However, the static effects may be con sidered for the purpose of the demonstration.

`Weights |05 and |06 are connected to themod'el, 1|" by cords |01 and |08, respectively, merely to illustrate the thrust and drag on the mod el .,in simulated flight. The cord |01 rides over a pulley' l-llllthat4 is rotatably mounted onV the frame member k`|-| and divides into a crowsfoot of, four y endsfto be attached to the four motor .nacelles 14;' -The cord |08 passes over apulley |`|.0 thatis rotatably mounted on the frameworkA member l2 and isattached to the model 1| at the trailing edge, ofthe airfoil 13. are 'only representative of the thrust. anddragl and are of insuiilcient moment 'to produce sub. stantial error in the indicators since a very slight, movement of the wing or tail portions of themodel'.- 1S Sufcient to actuate the indicators properly..

.load indicator frame. 30.

The. thrust and. drag' Weights mayl be disconnected'- from the model without dicated results.

From the foregoing it may be seen that there is providedl a.` simple and practical model weight and balance training aid for demonstrating the static effects from various loading conditions of aircraft. For the. purpose of demonstrationv it is as.. slimed. that the illustrated model airplane weighs 85,000 pounds and the C. G. is at 24% M. A. C. In the absence of any weight in the model 1| it lsshown by the` indicators that the wing load is 85,000. pounds by the wing load indicator, the tail load vindicator is atv 0 and the wing load attach... ment is. at 24% M. A. C. on the scale 05, 95. The rod or strip |0| could be disconnected from the tall andthe tail would neither rise nor fall showing that the model 1| is balanced with the rod or strap 85.011` the C. G. of the model when placed at 24% M. A. C;.of the scale 95, 95, a permissible location for the C. Cir. fory typical flying conditions. The 24..%M., A. C. isl verified by the needle pointerr 55 on thepercent C. scale 21 of the card 2,5. The. gross weightregistered by the needle pointer 551 onA vthe-gross weight scale 25 showing 85,000 pounds, also corresponds with the wing load in-4 dicator. Also the elevator is shown arbitrarily in astraight line trim with the stabilizer. Weights may be placed in the station compartments` 0| to representr thecrew, fuel, passengers, cargo, etc., andthe change in wing load, tail load if any, gross weight and thefposition of the C. G.k along the M. A.. C., if any.. will be represented on the indicaters.v VFor examplaweightsequivalent to 7,500 pounds placed inthe different forward station compartmentsfB-l along the fuselagesuch thatthe Wing load. indicator shows 85,000 pounds (upload), the tailload indicator shows a load oft-2,500` pounds (download), the gross load shows 92,500 pounds (8 5,000+!7,500 :95,000 2,500 92,500) and the C. G. location in percent M. A. C. would register, for example, 15% it would `befreadily understoodL that the nose of the model.- 1| is heavy to a; critical point because 15% M. A. C. indicatesthatthe C.` G. is now too far forward to allow safe flying conditions. In this condition of loading the elevator 18 will be deflected considerably upward since the upward pushfof the tail against the rod or strap I 0| places a countercluckwiserotative force on the lever arm |00 foroing the elevator 18 to rotate counterclockwise aboutl its pivot to demonstrate relatively the amount. of trim required to keep the airplane in level flight if such wouldfbe possible. The posi-l tion of the C. G. at 15% M. A. C. may be proved by rotating thev shaft 93.(on each section of the ailfQl. 13 `slflifting the hanger bracket 02 forward until the pointer 95 rests at 15% 4at which time the tail. load indicator will register 0 checking the. percent M. A. C. reading of the needle pointer 56. The shift of these hanger brackets bringing the tail load indicator to register 0 will causey the wing load indicator to shift position but. the indicated *gross load on the scale 25 by the needle pointer and the indicated C. G. position on the percent M. A. C. scale 21 by needle pointer 56 remains unchanged in value. That is, movement of the pointer toward the l5 in dication on the M. A. C. stale 904 causes the altering: the desirablev into rotate clockwise rotating the frame 24 clockwise also since the wing weight is being reduced by 2,500 pounds, butthis wing weight reduction increases the weight on.

thev tail by 2,500` pounds causing the tailyload frame.- 31. tu rotate.,counterclockwise andl conse,-A

wingr quentiy the pointer to rotate`y slightlyiclockwise simultaneously with the wing weight changesto maintain an indication of 92,500 pounds grossl weight and M. A. C. on the gross weight-M. y A. C. scales. The two scales 26 and 21 have been,

so plotted as to give true indications of the gross weight and the C. G. position in percent of the M. A. C. regardless of how the load to becarried is'distributed as long as the C. G. doesnot go Qutf side the M. A. C. scale.

On the other hand, the placement of weights in the station compartments 8l such that the wing load indicator registers 90,000 pounds (upload) the gross load indicator registers 92,500 pounds, the tail load indicator registers 2,500 pounds (upload) and the C. G. vin percent M. A. C. rose, for example, to 36%, it would be demonstrated that the tail is heavy to a critical point where the plane would not be safe for flying since the ac -v tual C. G. is now too far back along the M. A. C.

Also the elevator will be deflected downward a considerable amount to show the relative deflection that would be necessary if the airplane could..

be balanced demonstrating the relative change in elevator position for a typical level iiight condiA tion. The actual C. G. can be checked on the. scales 95, 96 in the same manner as set out above.

It is not intended that the deflection of the model elevator be quantitatively representative of the actual trim in full scale since other flight variables are involved. It is to be understood thatY in the foregoing examples the indication o n the wing and tail load indicators are the reactions that would be obtained if the airplane were supf ported at these points and at rest.

The effects of raising and lowering the land wheels 19, 8E may also be studied along with the,1

static effects of various loading conditions since their change in position alters the C. G. position* Although a certain specific embodiment of the invention has been shown and described herein,

it will be apparent to those skilled inthe art thatl many modifications of the application thereof,

as well as the details of construction, is possible without departing from the spirit and scope ofv this invention.

We claim:

l.' A weight and balance aircraft training aid j, comprising; a framework housing a wing load, indicator, a tail load indicator, a rotatable sector f card having gross weight percent lvl. A, C. scales thereon andan indicator pointer ope'rf@ ative over the scales of said sector card, thesaid wing load indicator and the said sector card being. operatively joined, and the said tail load indicatorA z and ile-e seid indicator pointerbeing operatively. joined; and means suspending a smallscale model airplane in the said framework, said means .com-

prising an attaching means between the .wing portion of the said model airplane and Athe said wing load indicator, and another attaching means between the tail portion of the said` mo del airplane and the said tail load indicator whereby weight distributed along vthe fuselage will dem Y onstrate the effects on the model airplane by indications of the wing load, tail load, gross weight and C. G. in percent M.A. C.

2. A weight and balance aircraft training aid. comprising; a framework housing a wing load iiidicator, a tail load indicator, arotatable .sector card having gross weight and percent M. A. C. scales thereon operatively connected .to and movable with the wing load indicator, and an indicator pointer movable across the scales4 of the sala sector card operatively connected to and actuatablenwith the tail load indicatonsaid sectorcard and indicator pointer constituting a single reading dual indicator for indicating the gross.. weight and C. G. in percent M. A. C.; a small scale model airplane having a neutrally biased elevator with a lever arm constructed and arranged to deflect the said elevator in an opposite direction to a force acting on the said lever arm;

a link connection between the wing portion of the said model airplane and the said wing load indicater.; and a link connecting the said elevator lever arm and the said tail load indicator whereby weight distributed along the fuselage of the model I airplane will demonstrate the static eiects on lthe model airplane by indications of the wing load, tail load, gross weight, C. G. in percentA M. A. C. and the relative elevator trim for iiight.

3. The combination as set forth in claim 2,

wherein the attaching means at the wing'portion A of the said model airplane comprises a hangen bracket adjustable along the M. A. C. of the said model airplane on which there is a pointer in indicating relation over a percent M. A. C. scale on the wing portion for adjusting the point of suspension at the C. G. along the M. A. C., and a rod pivotally linking the said hanger bracketl and the said wing load indicator.

4. The combination as set forth in claim 2,

whereinthe attaching means at the wing portionV of the said model airplane comprises a hanger bracket adjustable along the M. A. C. on which' is a pointer cooperatively associated with a per-y cent M. A. C. scale on the wing portion for adjusting the point of suspension at the C. G. along the M. A. C., and a rod pivotally linking the said hanger bracket and the said wing load indicator; and the attaching means at the tail portion comprises a lever arm attached to a neutrallybiased elevator of the said model airplane with the free end thereof extending forwardly and upwardly of the elevator pivot, and a substantially rigid rod linking the free end of said elevator lever arm and the said tail load indicator for indicating the relative elevator deflection to trim the airplane in flight. 5. 4A weight and balance cators housed in .the said framework, the said wing load indicator being operatively connected to rotate a pivotally mounted sector card in the said framework having gross weight and percent M. A. C. scales superimposed thereon upon operation of said wing load indicator, and

the said model airplane along the M. A. C., each bracket having a. pointer movable over a percent M. A. C. scaleon the corresponding airfoil to indicate the suspension point of said model along its M. A. C.; and a bifurcated rod connecting the said hanger brackets with the said Wing load indicator and a rod connecting the free end of the said lever arm with the said tail load indicator suspending the said model airplane in the said framework whereby the disposition of weight in the station compartments will demon-.

training aid comprising; a framework; wing load and tail load indlstrate the static eilects on the model airplane by registration of the wing load, tail load, gross weight and C. G. in percent M. A. C. on the indicators, and the relative elevator trim for flight conditions.

6. A weight and balance aircraft training aid comprising; a framework supporting a wing` load indicator means, a tail load indicator means, a rotatable sector card having superimposed gross weight and percent M. A. C. scales thereon, and an indicator pointer movable across the said gross weight-percent M. A. C. scales, the said wing load indicator means being operatively connected to the said rotatable sector card and the said tail load indicator means being operatively connected to the said indicator pointer for registering wing load, tail load, gross weight and C. G. in percent M. A. C.; a small scale model airplane having retractible landing gear under the fuselage and wings and having station compartments along the fuselage open to the exterior for receiving weights, a neutrally biased elevator with a lever arm attached thereto on opposite sides of a rudder fin and extending upward and forward of the elevator pivot to permit elevator deflection denoting relative elevator trim in flight for various tail loads, a hanger bracket in the airfoil adjacent and on opposite sides of the fuselage adjustable along the M. A. C. to permit adjustment of the C. G. position for various load conditions in the said station compartments and the retraotible landing gear; and two substantially rigid connecting means having a bifurcation on one end pivotally joining each the said hanger brackets with the said wing load indicator means and the said lever arms with the said tail load indicator means suspending the said model airplane to transmit weight and balance conditions to the indicators, said gross weight scale being so calibrated and the said indicator pointer being so connected to said tail load indicator that the gross weight-percent M. A. C. indication will always show the gross weight as being the sum or difference of the indications on the wing load and tail load indicators and the position of the C. G. along the M. A. C. Will always be indicated in accordance with the weight distribution of the small model airplane including its carried load.

' CLIFFORD F. DROWN.

NORMAN H. ZIMMERMAN. WILLIAM C. ROSS.

REFERENCES CITED The following references are of record in the le oi' this patent:

UNITED STATES PATENTS Number Name Date 1,906,443 Bisch May Y2, 1933 2,331,304 Carmody Oct. 12, 1943 2,391,243 Hutton Dec. 18, 1945 2,391,257 McWhorter Dec. 18, 1945 FOREIGN PATENTS Number Country Date 356,158 Germany July 17, 1922 

